The present invention relates to magnetically operated valves, such as fluid control valves. In particular, the invention concerns a fluid-tight flow control valve which includes a valve stem sealed within a valve housing that is magnetically actuated.
Magnetically operated fluid valves are known in the prior art which include an actuator movable between an on position and an off position in response to a magnetic field. For example, the patent to Halgreen, U.S. Pat. No. 3,326,511, discloses an electro magnetically actuated valve in which an armature is affixed to a valve stem. When an electric coil is activated, the magnetic flux causes the valve to move between an open and closed position. The Halgreen patent also shows a sealed cylinder in which the magnetic actuator and valve stem reciprocates in response to the generator magnetic field.
The patent to Cummings et al., U.S. Pat. No. 4,779,640, discloses a magnetically operated automatic drain valve. In the Cummings device, a float carries a permanent magnet that surrounds a closed valve housing. The pilot actuator reciprocates within that closed valve housing in response to the position of the permanent magnet relative to the pilot valve plug. Again, the Cummins et al. patent discloses an on-off type device.
The patent to Parodi et al., U.S. Pat. No. 3,666,231, discloses an electro magnetic valve which includes at least three windings which can be selectively excited. The selective excitation of the windings causes the valve to move between on and off positions depending upon which coils have been excited. Richeson, Jr., U.S. Pat. No. 4,831,973, discloses a similar valve that uses electromagnetic repulsion to move an armature. Bosley et al., U.S. Pat. No. 4,690,371, shows an electromagnetic valve with a permanent magnet armature. The valve opens or closes depending upon the electromagnet coil polarity.
Staefa Control System, Inc. of San Diego, Calif., manufactures a three-way modulating valve that uses an electromagnet oil to shuttle a valve disc between two positions to selectively connect one of two inputs to the output.
There is a need to provide a sealed valve assembly which can operate in response to a sensed condition. For instance, a flow control valve must vary the amount of fluid passing through a pipe in response to a fluid flow rate sensed down stream from the valve. The valve must be fluid tight so that the actuating member is free to reciprocate without risk of fluid leakage. There is also a need for a sealed valve that can be actuated in step-wise or continuously variable fashion, rather than simply an on-off manner.